The Evolution of the Atmosphere Flashcards
What is the composition f the current atmosphere? How long has it been like this?
78% nitrogen, 21% oxygen and small amounts of other gases (carbon dioxide, water vapour and noble gases)
200 million years
Describe earth’s surface and atmosphere initially (first phase)
Molten from many millions of years. It was so hot that any atmosphere just ‘boiled away’ into space
What happened next (after the molten stage)?
Eventually things cooled down a bit and a thin crust formed, but volcanoes kept erupting. The volcanoes gave out lots of gas. We think this was how the oceans and atmosphere were formed
Describe the old atmosphere (during the first phase)
Mostly CO2, with virtually no oxygen. There may also have been water vapour and small amounts of methane and ammonia (like the atmospheres of Mars and Venus)
What cause oceans to form?
When water vapour condensed
What evolved after the first phase? What did this cause?
Green plants and algae evolved over most of the earth. A lot of the early CO2 dissolved into the oceans. The green plants and algae also absorbed some of the CO2 and produced O2 by photosynthesis
What happened once some of the plants died?
They were burred under layers of sediment, along with the skeletons and shells of marine organisms that had slowly evolved. The carbon and hydrocarbons inside them became ‘locked up’ in sedimentary rocks as insoluble carbonates and fossil fuels
What happens the carbon when we burn fossil fuels?
The ‘locked up’ carbon is released and the concentration of CO2 in the atmosphere rises
What happens in the 3rd phase?
1) The build-up of oxygen in the atmosphere killed off some early organisms that couldn’t tolerate it, but allowed other, more complex organisms to evolve and flourish
2) The oxygen also created the ozone layer (O₃) which blocked harmful rays fr the sun and enabled even more complex organisms to evolve
3) There’s virtually no CO2 left now
